This invention is directed to a system for protecting the environment in the event of a loss-of-coolant accident in a pressurized water reactor which contains pumping and circulation equipment for radioactive primary cooling water outside the containment vessel for the reactor system.
Many systems have been devised for use in injection of coolant fluid into a nuclear reactor vessel in the event of a loss of coolant accident. Generally, the systems have means for sensing any break in the primary coolant system and pumps and valves to inject emergency cooling water into the reactor vessel to cool the nuclear core. The emergency cooling water, after contact with the core is to be collected, recirculated while cooled by a heat exchanger, and recycled for further cooling of the core, until the shutdown is effected.
Examples of emergency cooling systems for nuclear power plants are provided in the following patents. U.S. Pat. No. 3,649,451 teaches a containment system wherein a first quantity of coolant fluid such as borated water is used to fill a dry well containing the reactor vessel, to a level beneath the vessel, and a second quantity of coolant fluid from a loss of coolant source in the primary cooling loop is used to fill the well to a level sufficient to protect the core. U.S. Pat No. 3,702,281 shows a reactor system where the emergency water source is also a shield for the reactor and pumps for circulating emergency coolant water are provided outside the containment vessel. In U.S. Pat. No. 3,718,539, the containment vessel for the reactor is completely contained within an outer containment shielding structure which also contains a vapor suppression pool for condensing vapors released from the plant. Various core cooling apparatus are integrated into the system. In U.S. Pat. No. 3,859,166, a combined coolant storage tank and sump is located within the containment vessel, while pumping means for various cooling systems for the reactor are located outside the containment vessel.
The emergency cooling systems thus generally include a tank or other container for a supply of emergency cooling water, which tank can be located either inside the containment vessel or outside the same. Also, the heat exchange units for cooling of the recirculated emergency cooling water can be located either inside or outside the containment vessel. It is preferred, however, that the pumping means, a plurality of which are separately provided for assurance of operability, for use with the emergency coolant recirculation system be positioned outside the containment vessel so the routine checks and maintenance can be carried out on the pumping equipment in an environment separate from that of the containment vessel.
With pumping means located outside the containment vessel, potentially highly radioactive fluid would need to be recirculated in piping outside the containment vessel, in the event of a loss of coolant accident. If such piping, outside the containment vessel should break, radioactive fluid would be discharged to the environment. The fluid could flood equipment and instruments, and prevent access to an auxiliary building. While placement of pumps inside the containment vessel has been proposed, and has been used to a limited extent, to avoid any possible contamination due to pipe breaks outside the containment vessel, this arrangement does not provide any access to the pumps following any loss of coolant accident, and only limited access during normal plant operation.
It is an object of the present invention to provide a system for use in a loss of coolant accident, where the pumps for circulation of emergency coolant are located outside the containment vessel, while the conduits and pump through which the fluid is circulated could fail without contamination of the environment.